Musnad Ahmad Hadith 13403

Anas bin Sirin, may Allah have mercy on him, says that once we visited Anas, may Allah be pleased with him, on a Thursday. He called for a dining mat for us and invited us to eat. Some people ate and some refrained. Then, on Monday, we visited again, and he again called for a dining mat and invited us to eat as before. This time too, some people ate and some did not. Seeing this, Anas, may Allah be pleased with him, said, "Perhaps you are among those who fast on Mondays and Thursdays." The Prophet, peace and blessings be upon him, would sometimes fast so much that we would think that this year the Prophet, peace and blessings be upon him, did not intend to leave any fasts, and sometimes he would break his fast so much that we would think that this year the Prophet, peace and blessings be upon him, did not intend to fast at all. And the Prophet, peace and blessings be upon him, liked to fast in the month of Sha'ban the most.